Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention pertains to forming boards for a
paper making apparatus and more particularly to forming
boards which decrease the flocculation of the stock used to
form paper.
In the early practice of the art of making paper
by hand, the vatman scooped up stock from a vat by means of
a mold and then gave -the mold a series of shakes or "strokes"
while water drained out of the mold. The paper sheet which
was formed was very homogenous. Paper manuXacturers today
using automated machinery strive to obtain a paper sheet
which is comparable in uniformity, however most papers
manufactured by automatic means lack uniformity. Modern
studies have shown that one of the reasons for this lack of
uniformity is flocculation of the stock not only in the
headbox but also during the relatively short period of time
spent by the stock while it is on the forming fabric but
before it is formed. I-his flocculation has been somewhat
reduced by the use of rectifier rolls inside the headbox7
and transversal shakers disposed under the forming fabric.
~ 20 It has been found however that as the speed of the fabric is
`~ increased, these methods become less effective. It appears
that the vatman's stroke dispersed the flow of sto~,k by
inducing therein complex shears, and that in order to
produce high-quality paper at high speeds, new ~eans must
be found for emulating the stroke at high speeds.
Several methods have been suggested for breaking
up the flocs deposited or formed on the forming fabric, by
creating a turbulence in the stock. For example the Sepal
U. S. Patent No. 3,573,15g and Johnson U. S. Patent No.
0 3,874,998 have suggested forming boards having transversal
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channels for creating transversal waves extending across
the fabric. However these methods were still found to
be ins~ficient.
Recently Otto J. Kallmes and Manuel Perez have
suggested the successive generation and destruction of
waves which extend longitudinally wi-th respect to the
forming fabric as an effective deflocculation means for
high speed papermaking machines. This type of action forces
relatively large transversal movement of stock during the
forming process due to transversal shear thus breaking
up and/or limiting the formation of flocs therein.
Messrs. Kallmes and Perez' work was described at the 1982
Papermakers Conference, and published by TAPPI.
The objective of this invention is to provide
a forming board having elements which generate longitudinal
waves in the stock on a forming fabric of a papermaking
machine.
- Another objective is to provide forming board
elements which have a rel~tively simple shape, and therefore
are easy to manufacture.
Other objectives and advantages shall become
apparent in the description presented below.
According to this invention waves are formed
in the stock deposited on a forming fabric, said waves
being characterized by longi~udinal ridges and valleys,
by providing a plurality of forming board elements positioned
under the fabric J each element having an upstream transversal
edge with a plurality of spaced notches extending trans-
versally across the fabric. As the ~abric and the stock
travel across each board, the ~ater tends to drain through
the fabric and is ~orced back into the stock by these notches.
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Having thus generally described the nature of the
invention, reference will now be made to the accompanying
drawings, showing by way of illustration, a preferred
embodiment thereof, and in which:
Figures 1 and là show a Fourdrinier papermaking
machine incorporating the present invention;
Figure 2 shows a plan view of the forming board
elements;
Figure 3 shows a plan view of the forming board
elements having an alternate arrangement;
Figures 4a and 4b show cross-sectional views o~
the effects of the forming board elements
; of Figures 2 and 3 respectively;
Figures 5a, b, and c show details of the forming
board elements of Figure 2;
Figures 6a, b, and c show a second embodiment of
the forming board element;
Figures 7a, b, and c show a third embodiment of
the forming board element;
Figures 8a, b, and c show a fourth embodiment o~
the forming bo2rd element;
Figures 9a, bl and c show a fifth embodiment of
the forming board element; and
Figures lOa, b~ and c show a sixth embodiment of
~he forming board element.
For illustrative purposes the invention will be
:~ described in conjunction with a Fourdrinier paper-making
machine. As shown in Figures 1 and la, a Fourdrinier
machine comprises a headbox 10, a forming fabric 12, and
~0 breast and couch rolls 14 and 16. The forming fabric is
continuous and travels between the breast and ~he couch
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rollers. The stock is deposited from the headbox on the
top surface 18 of the ~abric. Immediately following the
headbox the fabric is passed over a forming board consisting
of several elements, 22, 24, 269 and 28. During this stage,
some water is drained from the stock and its fibers settle
in a thin wet sheet 20 completing the forming of the paper.
Following passage over the forming board the sheet is
transported past various other dewatering devices such as
foils and vacuum boxes. These devices are well-known in
the art and therefore are not described. At the couch roll
16, sheet 20 is removed and passed on to the pres~ and dryer
sections. The forming fabric is returned by rollers 30 to
breast roll 14.
Forming board elements 22-28 shall now be described
in more detail. It should be understood that while the
Figures presented herein show four forming board elements,
the present invention is not limited to only four elements
but is applicable to any number of such elementsO
As can be seen in Figure 2, ~orming board elements
22, 24, 26 and 28 are positioned transversal to the direction
of movement o~ the forming fabric indicated by the arrow.
Each element has a leading or upstream edge 32 on which
there is provided a plurality of notches 34. These notches
are preferably equally spaced along the length of each board.
As the fabric travels from the headbox, the water that drains
from the stock through the fabric is pushed by the notches
upwards back into the stock to form longitudinal waves therein.
A cross-sectional view taken slightly dolmstream of the notches
such as at line X-X of Figure 2 shows a plurality o~ waves
3 (see Figure 4a) comprising ridges 36 and valleys 38.
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- 4 -
~L2~X~
Each ridge corresponds to one of the notches 34. The
forming board elements may be oriented so that the notches
of each board are aligned with each other, i.e. two imaginary
lines A and B drawn in the longitudinal direction would pass
through respective no-tches 34 in each of the elements.
This alignment produces clear, well defined ridges and
valleys because, as the stock relaxes as it passes between
the elements~ it is pushed up again by the notches of the
next forming board element. This generation and re-enforcement
of longitudinal waves causes a transversal shear within the
stock which results in a transversal shift or migration of
the stock fibers which breaks up the flocs.
The transversal shear described above is increased
if each successive element phase shifts the waves transver-
sally instead of merely reinforcing it. This is accomplished
by positioning the second and fourth forming board elements
so that their notches are located halfway between the notches
of the first and third elements, as shown in Figure 3.
In Figure 3, the notches of elements 22 and 26 are
aligned along an imaginary line such as A while the notches
of elements 24 and 28 are aligned along an imaginary line C.
The effects of this configuration are illustrated in Figures
4a and 4b, wherein Figure 4a is a profile of the waves taken
along line X-X of Figure 3, somewhat downstream from the
notches of element 22, while Figure B is a profile of the
waves taken along line Y-Y downstream of the notches of
element 24.
A comparison of Figures 4a and 4b reveals that a
180phase shift takes place between lines X-X and Y-Y so
that the ridges of Figure 4a correspond to the valleys of
Figure 4b and vice versa. Ob-viously this effect can take
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place only if the fibers forming the ridges in Figure 4a,
such as ridges A and B move sidewise in the directions
indicated by the arrows to form the ridges C and valleys A
and B of Figure 4b. The process is repeated between each
successive board causing rapid transversal movement of the
stock ~ibers, and consequently, deflocculation.
The notches required to perform the above-described
functions can be of a plurality o~ shapes. Some of these
shapes are illustrated in Figures 5 through 10 and described
hereinbelow.
In Figure 5 the basic shape of the forming board
element is shown as having a parallelogramic cross-section
with the top sur~ace 42 having a leading edge 32 which is
more upstream from the leading edge 46 of bottom surface 44.
This shape is well suited for leading some water away ~rom
the wire as the wire slides across top surface 42. Notches
34 are formed by cutting pyramid-shaped pieces out of the
board. Thus a typical notch has two plane surfaces 48 and 50
which are angled with respect to each other and with top
surface 42. In this particular embodiment each notch 34 has
the shape o~ a triangular trench which narrows in the machine
downstream direction to a point 52 located on surface 42.
When fo~ming board elements of the type shown in Figure 5
~- are used in a Fourdrinier assembly the element leads some
of the water, which penetrates the forming fabric, away from
it except at the notches where the water is channeled and
pushed back through the wire by the trench to ~orm the
; longitudinal waves described above. The relative length,
width, depth, and spacing o~ the notches may be varied in
~o accordance with the speed of the fabric, the consistency
of the stock and the desired finish of the final producta
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~:2~2GO
The mode of generating longitudinal waves de~cribed
hereinabove in conjunction with the embodiments of Figure 5
applies as well to the o-ther embodiments described below,
unless otherwise noted.
A second configuration for the notch is shown in
Figure 6. In this embodiment, the notch is forrLed by
cutting a ~edge or pie-shaped piece out of the forming board.
Thus the notch has two side walls 54 and 56 which are
approximately perpendicular to -the top surface 42 and are
at an angle to each other to form an apex 58. The bottom
60 of the notch is approximately parallel to top surface 42.
In this embodiment as the side walls approach each other
in the downstream direction the water is again driven upward.
Figure 7 shows another embodiment in which each
notch comprises a rectangular trough having side walls
70~ 72, end wall 74 and a bottom 76. Walls 709 72 are
parallel to each other and perpendicular to top surface 42
while end wall 74 is perpendicular to both side walls and
the top surface. The bottom is parallel to the top surface.
This embodiment works in the same way as the pyramid-shape
notch of Figure 5.
The embodiment of Figure 8 is similar to the
pyramid-shape notch of Figure 5 except that the notch is
formed by a single curvilinear sur~ace generated by cutting
sections of circles perpendicular to top surface 42 with
decreasing width as the notch extends away from the leading
edge 32 ending in a po~nt ~0. Preferably to the curvilinear
surface is cylindrical.
In the embodiments of Figures 9 and 10 the waves
3 are generated by actually separating streams of water from
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the wire and then thrusting them back at the fabric 12.
In Figure 10, the notches are formed by making a rectangular
hole 82 through the leading side 84 and parallel with top
surface 42, and a second hole 86 drilled perpendicularly
through top sur*ace 42 to meet the rectangular hole.
Preferably the leading side 84 is made with a ledge 88 so
that as the water is being drained from the fabric by said
leading side, it is channelled by the ledge into hole 82,
and from there back to the fabric, via hole 86. Of course
this whole process takes place only when the fabric is
moving fast enough so that the water retains some of its
longitudinal momentum while being drained.
Figure 10 shows a simplified embodiment of the
configuration o~ Figure 9. In this embodiment, instead of
two holes, a single hole 90 is drilled between the leading
side 92 and top surface 42. Ledge ~4 is provided for
channeling the drained water back to the fabric through
hole 90.
In summary, the present invention provides formlng
boards with notches for generating and regenerating longi-
tudinal ~Javes through stock deposited by a headbox on
a forming fabric. The waves cause transversal shear within
the stock causing any flocs formed therein to disperse.
It is obvious that in addition to the embodiments
described hereinabove, other configurations can be made
without departing from the scope of the invention as
defined in the appended claims.
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